Effectiveness of cryotreatment of endocardial tissue is significantly affected by the contact of the catheter tip or thermally transmissive region to the tissue. Ex-vivo studies show a correlation between the lesion sizes created and the tip or thermally-transmissive region to tissue contact quality. A larger lesion size can be achieved with the same device by improving the tip to tissue pressure or contact. Various methods have been used to assess tip or thermally-transmissive region contact, using RF catheters and/or ultrasound imaging. However, none of these methods has proved entirely satisfactory.
The problem extends to all areas of tissue treatment wherein the tissue undergoes some change or “physiological event” during the course of treatment. In addition to contact quality assessment, in treatment devices that employ fluid flows, detection and containment of leaks is a critical problem, especially in the operation of cryogenic devices for therapeutic purposes, lest a leak of coolant enter the body and thereby cause significant harm. Known catheters which employ inflatable balloons often inflate the balloons to relatively high pressures that exceed the ambient pressure in a blood vessel or body lumen. However, to contain the coolant, these catheters generally employ thicker balloons, dual-layered balloons, mechanically rigid cooling chambers, and other similar unitary construction containment mechanisms. These techniques however, lack robustness, in that if the unitary balloon, cooling chamber, or other form of containment develops a crack, leak, rupture, or other critical structural integrity failure, coolant may egress from the catheter. To minimize the amount and duration of any such leaks, it is desirable to use a fluid detection system that detects a gas or liquid expulsion or egress from the catheter shaft and signals a control unit to halt the flow of cryogenic fluid.
Furthermore, since many treatment systems and methods are applied in internal body lumens, organs or other unobservable tissue regions, the orientation and attitude of the device structure relative to the tissue is of significant importance in ensuring the effective and efficient treatment of tissue. This applies to many tissue treatment systems, both surgical and non-surgical, using a variety of modalities, including cooling through cryotreatment, heat or electrically induced heating, ultrasound, microwave, and RF, to name a few.
This collection of problems may be resolved in part by developing a specialized transducer suitable for the “body” environment in which it operates. For many physiological events, there is no specialized transducer. The events in question include changes in the natural state of tissue, such as temperature, dielectric or conductivity changes, structural changes to the cells and cell matrix, dimensional changes, or changes in the operation of, or interplay between, tissue regions and/or foreign bodies, such as blood flow in an artery having a treatment device inserted therein.
All of these changes may be correlated to, or affected by, relative changes in the bioelectrical impedance of the tissue region.
It would be desirable to provide an apparatus and method of assessing lesion quality, monitoring and detecting any occurrences of fluid egress, determining blood vessel occlusion, determining tissue composition as well as assessing the quality of the contact between the tip or thermally-transmissive region of a cryogenic device and the tissue to be treated.